Television receiver horizontal deflection



SeptZO, 1949. H.SH/ \W 2,482,737

TELEVISION RECEIVER HORIZONTAL DEFLECTION Filed Mag 14, 1948 ll INVENTORATTO'RNEY Patented Sept. 20, 1949 TELEVISION RECEIVER HORIZONTALDEFLECTION Hubert Shaw, Drexel Hill, Pa., assignor to Radio Corporationof America, a corporation of Delaware Application May 14, 1948, SerialNo. 26,965

7 Claims.

This invention relates to circuits including magnetic deflecting membersfor controlling the position and rate of deflection of the beams incathode ray tubes.

While the present invention is broadly concerned with apparatus used intelevision transmitting and receiving equipment employing cathode raytubes as image scanning or reproducing devices, the invention does findapplication to apparatus of the oscillographic type used in observingrecurrent transient phenomena. More particularly, application of thepresent invention to modern television receiving apparatus results inadvantages which will be apparent as the speciflcation proceeds.

In television receivers employing electromagnetic deflection of thekinescope electron beam, it is the normal practice to employtransformers which suitably transform the low impedance of thedeflection yoke windings to a value of impedance into which thehorizontal and vertical output tubes may properly operate. Suchtransformers are usually quite bulky and heavy, and the cost oftransformers having designs adequate to handle the frequencies involvedin horizontal deflection circuits is normally quite high. In systemsusing a 15,750 horizontal deflection frequency, an output transformermust handle not only the 15 kc. fundamental, but also harmonic contentsup to at least the tenth harmonic of the fundamental, which trulypresents serious demands upon transformer performance. Accordingly, asystem which would provide sufiicient deflection for horizontal scanningwithout the use of an output transformer would be extremely desirableboth from the standpoint of cost as well as efficiency sincetransformers of necessity add considerable loss to the overalldeflection circuit. Another disadvantage which obtains through the useof a horizontal output transformer having no specific primary dampingand conventional secondary or yoke damping is that of Barkhausenoscillation which is a parasitic phenomena occurring within the outputtube due to the negative excursions of the output tubes anode whichexceeds the negative potential of the vacuum tube cathode. Barkhausenoscillation is well known to the art and is particularly undesirablesince it often occurs at a frequency which interferes with televisionreception through pickup by the picture IF or actual RF interference dueto beating with the local oscillator to produce interferring radiofrequency signals.

The present invention discloses a system wheredeflection signal outputtube, it is not only possible to eliminate the use of the conventionaldeflection signal output transformer and thus avoid those system lossestherein included, but such elimination permits the conventionaldeflection yoke damping to reduce the amplitude of the output tubesplate negative excursions to an extent that eliminates Barkhausenoscillation.

It is a purpose of this invention to provide a circuit permitting therealization of increased beam deflection efficiency in cathode ray tubesemploying electromagnetic deflection.

It is further an object of this invention to provide an improveddeflection circuit for kinescopes used in television receivers wherebythe tendency for Barkhausen oscillations in the output tube of thedeflection system is eliminated.

It is another object of this invention to provide an improved means forapplying deflection energy to an electromagnetic deflection circuit,wherein greater peak-to-peak deflection of the electron beam ispermitted for a given dissipation of energy within the deflectionsystem.

The invention will be understood from the following description taken inconnection with the accompanying drawing in which is shown an embodimentof my invention.

Referring now to the drawing, a Vacuum tube Ill having a grid l2 andplate electrode I4 is supplied with a series of synchronizingpulses It.The discharge tube NJ is connected in a conventional manner to produce asawtooth waveform of voltage across its plate resistor l8 according towell known principles of sawtooth discharge tube operation described forexample. A variable peaking resistor 20 is placed in series withcharging condenser 22 in order to provide a peaking control for thegenerated sawtooth wave shown at 24. The sawtooth signal 24 is in turncoupled through condenser 26 to grid 28 of vacuum tube 36. Cathode 32 ofelectron tube is connected through cathode resistor 34 to a negativesource of voltage 36. A potentiometer 38 is connected across negativevoltage supply terminal 36 and ground, and by means of variable tap 40thereon a variable bias voltage is made available through resistor 42shown connected to grid 28. The plate 4% of vacuum tube 30 is connectedto a source of positive potential as in typical cathode followerarrangements. The signal appearing across the cathode follower resistor34 is then applied to grid 46 of output tube 48, while screen grid 50 ofvacuum tube 48 is supplied with a positive potential through variableresistor 52 which is by, through the low impedance driving of the 5connected to a source of positive potential 54.

A suitable by-pass condenser 56 is connected from the screen grid 50 toground in order to stabilize the voltage appearing thereon. A deflectionyoke winding 58 is connected in series with plate 60 and positivepotential supply 54, thereby permitting the plate current of the vacuumtube 48 to energize the deflection yoke and cause deflection of theelectron beam in cathode ray tube 55. Damping tube 62 having a cathode64 and an anode 66 is connected across the yoke winding 58 to act as areaction dampingdevice. operating in a conventional manner.

Operation of the deflection circuit is substantially as follows: 7

A synchronized high impedance source of deflection signal is provided byvacuum tube [0, which is connected as a conventional sawtooth dischargetube. Sawtooth condenser 22 is permitted to charge linearily throughvariable resistor is from voltage source [9. Upon the arrival of asynchronizing pulse it, which is of sufficient amplitude to drive thetube 10 into heavy conduction, the condenser 22 is discharged throughthe resulting low plate impedance of the discharge tube. The rate ofcharge and the amplitude of the produced sawtooth is controllable bymeans of variable resistor 18, normally referred to as a size control.Peaking for the sawtooth deflection signal is accomplished by variableresistor 2c placed in series with charging condenser 22 and ground. Thepeaked sawtooth deflection signal appearing across the condenser 22 andground is coupled'through capacitor 26 to grid 28 of vacuum tube 30,which is connected as a conventional cathode follower type of amplifier.This amplifier when properly adjusted develops a voltage across thecathode impedance 34 which is an exact replica of the waveform contourapplied to the control grid 28, the function of the amplifier stagebeing to reduce the effective impedance of the source of sawtoothdeflection signal applied for driving the output tube 48. It will benoticed that since the cathode follower resistor 34 is connected to asource of minus potential 36, that a negative bias will be placed on thegrid 46 of vacuum tube 48. This bias will be equal to the magnitude ofthe negative potential supply 35 minus the D. C. voltage drop occurringin resistor 34 due to plate current of vacuum tube 3%. Since the platecurrent of vacuum tube 30 is controllable by adjusting potentiometer 38which controls the bias on control grid 28, this potentiometer alsoserves to establish the grid operating condition of vacuum tube 48.

An important feature of the present embodiment resides in the driving ofvacuum tube 48 from a low impedance source so that its control grid 45may be driven well into positive grid conducting regions withoutdistortion of the waveform as would necessarily occur were suchoperation attempted from a high impedance source such as presented byconnection to the sawtooth condenser 22. This permits the elimination ofthe usual output transformer for driving the deflection yoke, in thatthe deflection yoke 58 may be included directly in the plate circuit ofthe tetrode vacuum tube 48, which, due to the permissible increaseddrive of its control grid, is able to supply the necessary peak currentin the deflection yoke for deflection of the electron beam in cathoderay tube 55. Although the impedance of a practical deflection yokecannot be made sufficiently high to permit optimum normal operation ofpresently available output tubes, the reduction of maximum deflectionoutput power 'of the deflection system.

In accordance with well known practice, damping tube 62 in conjunctionwith its storage network 63 acts as a reaction scanning damping de-"vice'whic'h can be adjusted to provide up to 50 percentof the scanningphase of the deflection cycle. The energy to accomplish this is obtained-from the energy stored up in the magnetic yoke at the end of theretrace phase of the deflection cycle. This action is well known to theart and materially reduces the necessary conduction time of vacuum tube48 in supplying energy to the deflection systeml Accordingly, it isdesirable that potentiometer 38 be adjusted to provide a negative biasfor vacuum tube 48 which is'sufficiently negative toallow plate currentconduction in vacuum tube 48 for only slightly more than one-half of thedeflection cycle. When the adjustment is properly made, that portion ofthe deflection cycle not supplied by the reaction damping circuit, willbe supplied'for slightly more than one-half thedeflection cycle by theplate current of output tube 48.

It is important to note that the. practice of applicants inventionreduces the possibility of Barkhausen oscillations which occur in avacuum tube under conditions whenthe'plate element is negative withrespect to'its cathode. Since damping tube 62 has its 'cathode'filconnected to the plate so of vacuum tube 48, and plate 66 of dampingtube is in turn connected through the damping RC network 63 to platesupply source 54, it is evident that when plate 60 swings sufiicientlyin a negative direction, diode 62 will conduct and damp the voltageswing to the extent that the plate cannot swing negative with respect toground, thuspreventing Barkhausen oscillation. This deflection systemcan be adjusted to operate satisfactorily with a very, minimum ofnegative peaking applied to the deflection signal generated bydischarge. tube. l0. Since the requirement of negative peaking is toinsure plate current cut-off of vacuum tube 48 during the retrace phaseof the deflection cycle, the magnitude of the negative peaking requiredis proportional to the maximum positive voltage appearing on the plate60 of the vacuum tube. Since the high impedance of a transformer primaryis eliminated by direct connection to the lower impedance deflectionyoke, the maximum voltage swing appearing on plate. 60 is necessarilylower, therefore requiringless negative excursion of the control grid 46to effect cut-ofiof the tube.

From the above it is seen that a system suitable for controlled electronbeam deflection in such devices as monoscopes, iconoscopes, kinescopesand the like as may be incorporated in television receivers or otherelectronic equipment, and in so doing provision has been made for theelimination of the usually included deflection system outputtransformer. As a result of this, it is found possible to orient theusually present damping tube so as to eliminate Barkhausen oscillations,which are extremely undesirable in modern systems.

What is claimed is:

1. In a deflection system for a cathode ray tube having a deflectablebeam of electrons therein, a primary source of deflection signal, afirst and second vacuum tube, each having a cathode, an anode, and acontrol grid, 'a circuit communicating the deflection signaluderivedfrom said primary source to saidtfirst-vacuum tube control grid, animpedance connected in the cathode circuit of said first vacuum tube toprovide a secondary source of deflection signal, an electromagneticdeflection: yoke having a winding, said yoke being adapted to causecathode ray beam deflection upon excitation of said deflection winding,a circuit connecting said yoke winding between said second tube anodeand a source of energy for said second tube anode, a third vacuum tubehaving a cathode and an anode, a connection between said third tubecathode and said second tube anode, a connection between said third tubeanode with said source of energy for said second tube anode, and acircuit connecting said second tube control grid to said secondarysource of deflection signal so that variations of said yoke windingcurrent will have greater peak-to-peak values attendant with morefaithful conformation to the contour of said primary deflection signalwaveform than would obtain if said second tube control grid were drivenby said primary source.

2. In a cathode ray deflection system employing electromagneticdeflection, an electron tube having at least a plate, a cathode, and acontrol grid, a magnetic deflection yoke having an electromagneticwinding, a circuit for connecting the said deflection yoke winding inseries with said electron tube plate and an energizing source ofpotential, a high impedance source of deflection signal, a cathodefollower circuit for converting said high impedance source of deflectionsignal to a low impedance source of deflection signal,

means for connecting the low impedance source of deflection signal tothe control grid of said electron tube such that the driving impedanceimposed across the grid is sufliciently low to permit driving of saidgrid well into grid conducting operation, whereby improved and moreefficient operation of said deflection system results by merit of thelow impedance source of excitation so provided.

3. In a cathode ray deflection system employing electromagneticdeflection, a vacuum tube having at least a plate, a cathode, and acontrol grid, a magnetic deflection yoke having an electromagneticwinding, means for connecting said deflection yoke winding in saidelectron tube plate circuit, a source of deflection signal, a secondvacuum tube connected in a cathode follower circuit connected forconverting said source of deflection signal to a lower impedance sourceof deflection signal, means connectin the lower impedance source ofdeflection signal to the control grid of said electron tube such thatthe driving impedance imposed across the grid is sufiiciently low topermit driving of said grid well into grid conducting operation, a thirdelectronic vacuum tube having at least a cathode and a plate connectedacross said deflection yoke so as to provide damping storage releaseaction, whereby the operation and efliciency of the said deflectionsystem is improved by said merit of the low impedance of said drivingsource for the first electronic vacuum tube.

4. In .a cathode ray deflecting system employing electromagneticdeflection, a high impedance source of deflection signal, meansconverting said high impedance source of deflection signal to lowimpedance source of deflection signal such that said low impedanceprovides a driving source of voltage for sufiicient excitation of afirst electronic discharge tube having at least a cathode, a plate, anda control grid, an electromagnetic deflection yoke having a windingconnected in series with the plate circuit of said first electronicdischarge tube, a second electronic discharge tube having at least acathode and an anode connected in damping relationship to saidelectromagnetic deflection yoke, whereby the low impedance of thedriving source of deflection voltage for said-first electronic dischargetube is such as to permit operation of said first electronic dischargetube int-o an extended region of control grid current whereby theimproved operation of the deflection system is permitted by merit of thepermissible operation of said first electron discharge tube in the gridconducting region due to the low impedance of the source of deflectionvoltage,

5. In a deflection system for a cathode ray tube having a deflectablebeam of electrons therein, a primary source of deflection signal, afirst and second vacuum tube, each having a cathode, an anode, and acontrol grid, a circuit communicating the deflection signa1 derived fromsaid primary source to said first vacuum tube control grid, an impedanceconnected in the cathode circuit of said first vacuum tube to provide asecondary source of deflection signal, an electromagnetic deflectionyoke having a winding, said yoke being adapted to cause cathode ray beamdeflection upon excitation of said deflection winding, a circuitconnecting said yoke winding between said second tube anode and a sourceof energy for said second tube anode, and a circuit connecting saidsecond tube control grid to said secondary source of deflection signalso that variations of said yoke winding current will have greaterpeak-to-peak values attendant with more faithful conformation to thecontour of said primary deflection signal waveform than would obtain ifsaid second tube control grid were driven by said primary source.

6. In a cathode ray deflection system employing electromagneticdeflection, a vacuum tube having at least a plate, a cathode, and acontrol grid, a magnetic deflection yoke having an electromagneticWinding, means for connecting said deflection yoke winding in saidelectron tube plate circuit, a high impedance source of deflectionsignal, means converting said high impedance source of deflection signalto a low impedance source of deflection signal, means connecting the lowimpedance source of deflection signal to the control grid of saidelectron tube such that the driving impedance imposed across the grid issufiici-ently low to permit driving of said grid well into gridconducting operation, a second electronic vacuum tube having at least acathode and a plate connected across said deflection yoke so as toprovide damping storage release action, whereby the operation andeificiency of the said deflection system is improved by said merit ofthe low impedance of said driving source for the first electronic vacuumtube.

'7. In a deflection system for a cathode ray tube having a deflectablebeam of electrons therein, the combination of, a primary source ofdeflection signal, a first and second vacuum tube each having at least acathode, an anode and control electrode, a circuit communicating thedeflection of said second tube !to receive deflection excita- 10 tiontherefrom, and a circuit for coupling said second tube control grid tosaid secondary source of deflection signal so that variations of saidyoke winding current will have greater peak-to-peak values attendantwith more faithful conforma- 5 tion to the contour of said primarysignal waveform than would obtain if said second tube conrtrol electrodewere driven by said primary source.

HUBERT SHAW.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,074,496 Vance Mar. 23,19372,182,608 An drieu .'.....d Dec. 5; 1939 2,439,321 Starr Apr. 6, 1948

